Limiter system



Dec. 9, 1952 G.J.C.ANDRESEN LIMITER SYSTEM Filed March 29, 1947 3 Sheetg-Sheet l G. J. c. ANDRESEN LI'MITER SYSTEM Dec. 9, 1952 3 Sheets-Sheet 2 Filed March 29, 1947 i OUT/IIT ATTORNEYS DSC 9, 1952 G. J. c. ANDRESEN 2,621,290

LIMITER SYSTEM Filed March 29, 1947 3 Sheets-Sheet 5.

@www MM ATTORN EYS Patented Dec. 9, 1952 UNITED STATES PATENT f GFF ICE f ":2;6 21,290 L i 'LIMITEE` SYSTEM vGilbert J. .10. Andresem vStow.0hio;l Application-March 2.9, 1947., vSvlxiltlillo' 7385165 17 Claims. l

:This invention relates toazlimiter system` for `effectively reducing. static.. andy lnoisel and the-.like

interference. -in 'the reception of radiol .signals and ,is 1.a continuation in *part .of my copending f application, Ser. No. .-606,415, led .July` 21,? 1945,

which matured .into U. S. Patent No'. :2,418,389 on April 1, 1947.

The principal object of theginventionvis .topraand noiseginvperiodsgof'strong static.,fparticularly 'during .,thei reception ortrelatively weaknisignals.

z .The-.invention :is particularly :adapted fori use in;-the-.;reception of :voice modulated"-carriergsignals l.to improve'thezclaritrcofspeech which-other- -wisecwould .be distorted,V -or'fpartially or wholly vmasked, bythe interference.

' In accordance with the inv.ention, antimproved -videa lirri-iterfwith:whichV discrimination may be attained, within reasonablelimits, lbet-Ween.'signa'l system is iprovided 'comprising; in z-.combination several .component electronrtube 'circuits-and alrfrangements,.somefoffwhich are 1broadlyolddrnthe art, others specifically; new.

.A' feature ofrthe `invention :istheiprovisionz-o'f both direct and inverse: couplingiorfsignal'mnd static-from the signal detector tothe audio system @of a-.receiver-.in .suchmanner'thatz thezstatic peaks 'are'.not only limitedibutz are also inverted.

A preferred embodiment of: the 'invention` includes a pair of electronztube:rectiiiers-wvliich arebadapted to supply half-Wave y'rectiiication ycomponents of radio-frequency carrier and modulation to .an electron tube lreversing;repeater for producing an opposite-polarityfreplicaof-isaid components, two coupling circuits (directa-nd inverse) for coupling the oppositepolarity recti- -cation-components, a limiter tube inreachoi.' said'coupling-circuits, means for establishing gate `voltagesy determining the V-cutcii levels yof "thelimlputtozthe audio'fsystem voi1'a'iadio receiver. A complete Vunderstanding .of-.the improved system rand the mode :of operation of thefseveial component .electron tubes 'andfcircuits-fof thefinv-ventionfvvill be had by reference tozthe followingdescription and to .the-drawings; to be .cnsidered'in,.conjunctiontherewith;

vIn-the-:drawings:

' Fig. lisafcircut: diagram1illustratingthel several component electron tubesand-the circuit arrangements :of a preferred "embodimentofthe improved system;

x Fig. `2 shows a modication of vthe system" of Fig. 1;

Fig. l 3v showsA a- `simplified analysis voffthepsignal rectifier of Fig. 1;

Y yplinjg.y Although -,-an y convenient. signal frectifier may be used, the rectier shownvhasfspecialfadvantage-s amongA which is the. ability tovaryfgthe output lcharacteristics,.-cur-.ve as will .beflaterdifslcussed. iThe rectiiier ViA,- a-.triode, risrconnected .aswa'diode to the ,signaleinput circuit comprisingr the transformer secondary lvl'andthe .tuning capacitor Illa, with its cathode -|I connected .to the pointil 2, .and its @grid I3., .which ,serves aszone diode anode, .coupled tofthe point [-4 through -resistanceda, -24band electron .tubefrectiiier fl/na. This :rectier Vu; Viis-'a -coupling 'valveand is used to lfacilitate:neutralization ,in conjunction'y with .neutralizatingcapacitors 2|;, 122,and 23 fas will be fexplaineclcmore ini-:detail later. The Aplate =.I 5

:of'tube- Vizi. which serves-asanotherxdiodefanode,

is connected to point I 4 through resistance :Il andrectier'ftube Vm.- ,Capacitances-ff Ha and'la lare-.connected lin parallel .respectively to resistors iHsand 24u; y2llb;.botlll of which are connected to .ground I6.

1The tube;V1-A- supplies aha-lf .-wavesnofvradioefrclquency carrierfandmodulation 'of thesignalfas a negative potential 'f-fEg, tothe .control element :20 \.of.zelectron tubel/Tz, :a radio-frequency limiter and amplifier 1- :which-serves also.l as"v :a reversingifrepeater..

. :Directing attention.- specically towtheatubez-Via VVof Fig-1111, 'z'.the; =.ca,thod`eto'p1ate andz cathode-:togridzload resistorsllffand 24a'thereof provide leakagerpaths of;.lt1igh` resistance' for'stheuxsignal andl :station ,voltages 'which .are rectified in: this tube. The rectified 1, -half -wavesappears across these 'resistors ,'and-:arepreserved in :isome-z degree vby making the shunt;- capacitance Hav fand: 20a rather small, @perhaps :only: the inherent: capacitance ofl the circuit elements.

The instantaneous relationship ;o,f;.tl1el various voltages. and currents are affected. by` thesanode land grid resistance-capacitance .(RC)A .timer constants which, vgreaterrftlmn .one-half" the carrier period, accumulate substantial fnegativebias potentials onfzthe n.diode anodes of "tubeVr-A, rof magnitude .-proportional lto the amplitude of `the voltagefrom .theinput circuit.

To. obtain the fastest response .in the-rectification ofthe carrier-frequency lvoltagefromthe input circuit, the RC time constant of the `.load .of-each` diode ismadexlessthan the timeinterval or pulse'width of.Y theshortest -pulseof4 noise, as determined by, .the preceding selective circuits in the receiver. The stray capacitance of the wiring-.connections and .the tubes .and-additional 3 capacitance, if present, will Inot seriously affect the performance, provided the -time constant does not exceed the rminimum pulse width.

The preferred RC time constant for one-half` cycle Would be RC--l/gf, in which ,f is the frequency of the voltage applied to the rectiliers.

Referring again to Fig. 1, and in particular to the rectifier load 24a, there is sometimes developed at the point -Eg an undesired amount of negative potential caused by electron flow. To counter- .act that undesired condition, a divided load resistor 24a, 24h is provided and a Small opposing current is supplied in resistor 2da through the resistor 25l from the power supply voltage source I +En If it is desired to provide the usual grid bias on the tube V2, a' cathode resistor 68 may be `employed as shown in Fig. l. If a resistor SQ of proper value is used, resistors 24h and 25 may not 'be required. The negative feedback action 'of the voltage drop across resistor 6D serves toreduce distortion and to permit a: higher input voltage to be appliedto the controlelement before age from the rectifier. I

Itis'not necessary to control tube V2 with the resultant sum of the half waves. V It may' 'be prefferab'le to actuate thefco'ntrol electrode 2U thereof by the voltage of '-'each increment. '-Inthat case, uthe' internal resistance of V2 should b'e restored quickly to its nO-Signal value between' thelhalf- Wave conducting phases of the'rectierto assure lthe fast operation which is required'to" follow static pulses. l i

' Therepeater or amplifier tube V2 is provided with the usual plate coupling resistor 29 between the plate and a source of fixed positive vvoltage -i-Ez. This voltage is assigned the least value "which permits this repeater to function over a VWide range of signal strengths; its small voltage prevents the static pulse amplitude from exceeding i a limited amplitude 'preferably 'not' much greater than the peak amplitude of `thesier'ial.

As explained hereinbefore, in the absence of .signals the preferred voltage'onthe control elec- -trode 2D! is zero'. During the negative half-cycle :ofthe signal, the' control-electrode' voltage'is negative and of a value directly proportional to the amplitude of the radio-frequency voltage'ap'- plied to the rectiiiers. During the 'positive halfcycle of the signal the control-electrode voltage should'be Zero or preferably as `near-1 thereto'ia's it is possible to attain'.` "Thus the rectified voltage output -l-Es from the repeater'tube' V2' is limited by the voltage E2.

The outputA of the half-cycle radio-frequency Ai'roltage -l-Es includes the rectified modulation of Athe carrier, and when the half-Wave increments ,thereof are impressed upon an audio system the original`v modulations are reproduced.

The repeater tube V2 is preferably ofA the variable-mu type and is, therefore, adapted to operate with a high voltage input. However, a conventional triode tube, screen-grid tube, pentode or beam tube can be used. The pentode or beam tube, for example, would provide satisfactory limiter or cut-olf characteristics if the 'input and element voltages are held Within limited Value The positive voltage E4, which is a manually rectifier tubes V4 and V5.

the foregoing, the limiter system proper and its mode of operation will now be'discussed.

-to its clipping action.

adjustable fraction of thel fixed positive voltage 'of the-source -l-Et, is the gate voltage which determinesl the cutoff levels in the series-limiter For any desired value of signal intensity, the voltage E4 is adjusted so that the limiter V4 cuts off at the level of greatest outward modulation, preferably the level corresponding to unity modulation so as to preserve the desired modulation and cut off only the excessive peaks of noise... With the same adjustment, the other limiter V4 cuts off at the level of greatest inward modulation. While not ordinarily required, of course a separate adjustment corresponding to E4 could beprov'ided forthe second limiter V5 to meetspecial requirements.

With proper adjustment of 4E4 the limiter V4 stays closed for the normal range of modulation, but opens up on peaks of greater amplitudesuc'h as strong pulses of static. '-'jf The various elements having been explained in A'While the clipping of 'static 'pulses is known to'be a great aid in reception, this invention gains -a major advantage by a further action, namely,

inversion of 'the Vstrong pulses which otherwise would cause the loudest'residual clicks. The 'inversion requires two coupling paths for rectied modulation from the detector to .the limiter. The rst is a direct coupling path, which predominates -in the amplitude range of normal modulation but 'which is cut off at greater amplitudes.

The sec:- ond is an inverse coupling-path which predomi- 4nates' vat greater amplitudes and causes inversion ofthe peaks'of strong pulses.

In Fig; l, the so-called direct pathl is through the repeater V2 and biased limiter tube V4."-It conveys the" desired modulation in what may be called the positivev senseand but forythe limiter V4 would conduct the static peaks. The inverse path which also conveys the desired modula- -tion and static peaks but at a lesser'amplitude,

is through the capacitor 45 and resistor 44, and around the limiter V4 so this path is not subject Now considering the performance toward "a signal accompanied by' strong pulses of static, the pulse peaks coupled topoint for example,

by 'resistorll and capacitor '5 from Ep predominate at--instants when the tube V4. is'cut-off. The staticl puisefvoltage is weakly coupledto point-d2 so that theanode voltage-ofV4 becomes 'less positive, cutting olf further-passage 'of the stati'cp'ulse through V4. The value of resistor '44 should be such that'strong static Will not modulate th'e voltage at point 42 beyond the zero axis value of the signal while unmodulated. The capacitor 45 should be of sufficient value to prevent any'substantial'phase shift vin the passage Y of the pulse current from -Ep to point 42.

Asv insurance that the inverted pulsepeak will not recede past the Zero axis of the modulation,

lthere is added' a second electron tube limiter V5 coupled by capacitor 41 to V4 and having a sepa'- rate` gate voltage. The limiter V5 is adapted to operate and limit on the 'inverted peak of a strongstatic pulse.

The output of V5 has a time constant determined by resistor d8 and capacitor 49, of the same order of magnitude as the period of the highest modulation frequency to be reproduced. The ad'- vantages gained by the use of limiter Vs as 4just described, are that the coupling of the inverse peak of the static pulse can be increased to obtain a more precise limiting thereof. 'v 'i' reasonthat the"timeiconstant'of-'48, 49i==effective at-jpoint SZ-Will not permitthevoltage-fon-"the cathode of V5 -t'o-icllow-thesudden-l inversefpea-k at' pointv 43-. Before equilibrium can bef I'estab- Llished betweenfpoint 52 'and-point 4'3; tube'V4 "has cut off in `the mannervr explained hereiiibefore. -Thismode' of -foperation1=eiTects a 'very 'fsharp f cut-off' rof `thestatic `pulse because :the inverse `coupling may be-increasedto-fpermit thefeffective `useof rapid' charging ofthe vsmall l--interelectrode capacitance, wiring connection capacitancer etc., 'of -the `limiter tubes V4 and V5. f'During the static pulse interval the'limiter beftween points 43 and 52fprevents f the :inverted peaks from passingf-tl-iezero-axis value of'the signal modulation. This is. adesirable mode of operation because the inverted ,peak amplitudel is Withinn the range of normal modulation.`

When:` the.v static pulse voltage #has f decreased from its .peak toa value where point .4l becomes negative with respect to point 42, the limiter V4 becomes'conductive and V5 is already4 conductive so the normalresponse to modulati'onis resumed. In theabsence .of la static pulsethe lirnlters V4 and. Vsremain conductive to signal amplitudes ofv the fullrange determined by the gate voltage E4. Y The operation of thelimiter as aawhole will be summarized briefly with reference to the essentialfunctions of some parts vof the circuit as described above. The principal parts are the signal detector including tubes ViA and V113, the re `I versing amplifier'including tube V2, the inverse".

coupling path including resistor 44, the limiter includingv tubes Vr and Vs, and, theadjustable gate-voltage E4.

The signal detector utilizes the rectier :tube Vm to deliver rectied signal voltages of negative polarity from electrodes-t3 and I5, both acting as anodes. The vother rectifier tube Vm is needed only to'preserve-the potential at point I4 during the non-conductive phase of Vmand thus permit neutralizing capacitors 22 and 23 to be effective.

The reversing amplier utilizes the tube V2 to-reverse-and-amplify the rectied signal received from electrode I3 of the detector.

Infthel usual mannenth'ei signal is"v reversed in this amplifiery so the amplified signal coupled .thrdugh :the: capacitor 40 may -befregarded vas spositive; meaning that 'outward-modulation ofw-V 'limitei'sg'it isfterlned-thefdirect coupling circuit'- inf vcontradistinction to ftheinverse Vcoupling cir-A cuit-now to'be identied.

*The* inverse couplingfcircuit utilizes -resistor 44 to Acouple to the "limiter lthe rectiiied sig-nal received-f1om--electrode l'of'` -the detector: `ThisVV -signal"is"negativein polarity; and is 'therefore-A inverse relative tofthe positivesignal output `from the amplifier; VThempurpose of"this cou `pling will'be"further"summarizedV below. The"lim'iter*includes twoaectier tubes con-`4 `nected -in series opposition -for limiting the signal in vboth directions corresponding to--outward and 'inward modulation.

'.Fhef," amplied signal is coupled from the anode of tube V2 through the capacitor 40 :to the limiter.

The lfirst `tube V4 is poled -A'to "cutoff beyond acertain' level of' outward mode ulation. v The-secondtube 'Vsis poledloppositely v6 tefcut ofEibeyond-a' certain flevellof `inwardfmodu lation. f When apeak ofthesignal envelope, for: example afstatic pulse; hastal peak .voltage exceedingfthe 5 cutoff-level for-outward modulation, as dened above, itfis 'applied with. positive;v polaritymo point -4l 'and *the cathode of limiter tube V-4,. and.fcauses 'this' v7tube Atofbecome non-conductive.- Therefore the-peak of kthis ypulse is' not -coupled in: this: tube throug'hethe limiter. However,.f-thefinverse couplingfpath through resistor 44'issti1l-operative onthel peak of such a'pulse and 'couplesfthe peak with reverse polarity tothe. point 42 inthe-limiter, detouring around the tubeVi whichis'cut 01T; 'Therefore-'the'peak of "the pulse=appears inverted finfthe output of the-limiter so the `peak is actually at alevel lower thanthe above-identi? edjctoi level forv outward modulation.'V vThisis 'one 4of the principal advantages of tthe present l*invent-ion; Abecause therebyl the reflective peak amplitude of a" lstrong," 4pulse is "actuallyireduce'd vto Aa fleveliless. than the level at.. which thejhghest `signal vpeaks of modulationl are 'permitted topass withoutdistortion. It. is desirable that the .inversestaticpulse should 4notindent `the signal 1to0 far;` The ,second rlimiter vtube V5 achieves'jthis purpose :bylimiting any excessive peak' values of inverse pu1se's. Furthermoraby relating. thegtime constantof resistor 48 and capacitor dlfinthelimiter output circuit.

to fthehighestmodulation frequency, the. limiting .leve l for pulses ofjshort durationofleither signal yor static can be'reduced.withoutdetriment toithe desiredmodulation components offlowerffrequericiesandqmaximum u amplitude.` The clipping, o1 vshort pulses lof lmodulation at va. level-.lowerflthan .lowffrequency .components y of lmodulation iepermissibler becausecthe ydesired Imodulatiorr-..seldom includes short pulses of strong modulation.. NiThemanuallyqadjus-tablewdirect yvoltage vE4 is the .gatefvoltagevv which 'isi-,applied to the-ilimiter tubesV Vr-and Vs ftedeterminel their clipping lor Ylimiting levels, fas.described above.

i `Izrthedoregoing deseriptiorrfitispresumedzthat fawstronglpulse.fofstaticrsuperirnposedfon af'modu- I fiated-carrierzhas V1all! fth erv'appearances; offa spulse of@'modulaftionf; zthat t is; 'an :excessivexpeakiinuthe modulaticny .zenvelope As 'statici-pulse :is disting- .g'uished only :if itsnpeak amplitude *.exceedscithe :ther presentinvention: :minimizes itsifdisturbing `tefect byreducing iter-peak value as :iit'remrains .ixrtheoutput'of the limiter.

-uilllustrativecircuit ,constantivaiues .fand-types ofielectron` tubes yf orA the successful vreception l of -voice ffinodulated `signals .tlirough .both atmosf- -fpheric :static `andflocallyfpro ducednoisesfxare -set iortli'be'lovn Load caoacitauces usual1y ,ll1hercnt straws- `:anpuoximately 10 puf.

rmodulation Fpeaks of Lthesigna'l': In thatsca'ser Ain Fig. l.

-used on the same elements in Fig. 1.

Fig. 2 shows a modification of the arrangement of Fig. 1, in which a simplified detector circuit is employed to deliver both'polarities ofrectified signal, and in which the dual function of the limitertube V5 is performed separately by two tubes with some advantage in performance. Corresponding elements are designated as in Fig. l.

The signal detector or rectiner function is perfonned by the diode tube Vi. Its load comprises the-three resistors, |83, |64, |05, bypassed for radio `frequencies by the condensers mi and |02. Rectified voltages of both polarities are developed respectively at ES across resistors |03 and |64, and at +Es across resistor |85.

The direct coupling of the signal from the detector to the output is from the tap between resistors m3 and |84, through the series limiter -tube V4, the coupling condenser 59 and the output voltage divider 56. The cutoi or clipping level in this path is determined by the current from f -the source of direct voltage Ens through resistors |03 and |9 and the diode V515. By selection of the value of this voltage, this cutoff level is set at or near the level of outward peaks of maximum modulation. Y

The inverse coupling path is from the signal .voltage ,-i-Es through the limiter diode Vai., the coupling condenser |01, the resistor |09, the diode V512, thecoupling condenser 59 and the output voltage divider 56. A novel feature of this arrangement is the connection of a source of voltage ,+En through resistor |06 so chosen that the diode V55. permits coupling through the inverse path only during pulses of strong static which exceed the signal modulation, but not during normal modulation. It is therefore not necessary to restrict the amount of coupling in the inverse path so severely and the inversion'of pulse peaks can bel accomplished more abruptly by more inverse coupling.

Fig. 3 is a simplified diagram, omitting neutralization, of the special form of rectifier shown This rectifier consists of two diodes both simultaneously rectifying the same half waves. By choice of suitable circuit constants for each rectier, this double diode rectifier may `be madeto give a practically linear rectifying Acharacteristic or a characteristic which varies from linearityin either direction' as illustrated the parts shown in Fig. 3 bear reference characters corresponding to the reference characters If the plate 5 and leakage path I1, I'Ia are removed,

the remaining elements I3, with leakage path 24a, 24h, 20a, function as a conventional rectifier. The cathode-grid resistance Rg is not substantially affected by the plate current if the input voltage E2 is held at the same relative potential when the plate load is removed. However, the value E2 will be lowered as the impedance Z3 begins to draw additional current from the source impedance Z1, and the. increased current will result in a voltageloss.

The total rectiiier impedance Z2 is the parallel resultant of the output impedance Z5 of the diode rectifier Il, I3 and the variable'shunt impedance Z3 of the diode rectiiier- I5. The arrangement thus operates in eiiect as a variable impedance rectifier, the Z3 impedance characteristie of which may bepredetermined by proper selection of the plate characteristic Rp.' and the load impedance Z4. The input voltage characteristic may be given a downward slope to compensate for the characteristicof .output 4voltage signal voltages are present.

8 Eg. If a downward slopeof Eg is desired it may be attained by decreasing Rp or Z4, or both.

The resistance load Rpi. (|1) and capacitance Cp (Ila) develop the negative potential -Ep providing a delay bias for the conductive phase of the anode. The cathode-to-grid current is independent of the anode current if the input voltage E2 is constant. Since the grid voltage Eg affects the anode current, no plate or anode current will flow until the negative diierence between -Eg and the cathode input voltage En is less than the grid bias required for plate current cut-oir at the instantaneous plate voltage (E2-Ep).

The following equations expressed in terms of the symbols appearing on Fig. 3 will permit ready analysis to be made of the various voltages and currents of the rectier:

E2 Ep a/z K E2 E,+ GMR. When (Ez-Eg-l-EV-E) is negative, I=zero (0) GmRv When` (E2-EQ is positive, I,==

E E 3/2 Y K(E2E,+ ,MRUP) Kw2-Edif When (EV-Eg) is negative or positive, I

EH. Evy/z K E2 E, -GmRp When EV-E., GmR.,

j (Er-Efiis negative, I.1=zero (O) vpotentials and electron velocities at the grid and anode, I3. c

Fig. 4-illustrates the relation between rectier input voltage E1 and the output voltage Eg. Curve A- is that of a non-compensated rectifier showing the output distorted by reason of increased eiciency at the higher input voltages. Curve B is that which may be attained in the improved system with the downward slope of Ez effected by proper choice and proportioningy of internal and external impedances. It may be made linear and distortion-free by careful choice of these impedances. Curve C is an output curve having a logarithmic characteristic and the downward slope thereof is useful when strong The distortion in this case is not greater than that had with a conventionalrectier, and is to be preferred to that caused by anoverloaded amplifier with a `rectifiercharacteristicis. adjusted to be substantially as in curve. .B of Fig. 4,. the resultant negative vvoltage .impressed upon control element; 20

of tube V2 will .produce :an output current'characteristic substantially as in C, .ai substantially linear- .relation with respect .to the radio.- frequency input voltage .-..Eg, In .other words, the.:curvature .of rectication in tube 'Vm will compensate for the curvature of ampliiication 1in tube V2 to effect a linear response to modulation -of the input signal.

Referring again to Fig. l,` and in particular to the tube-Vm thereof, it is to be understood that the stray capacitance of wiring and the internal capacitance of the tube provide a radio.- frequency coupling path across the rectifier, which istheprincipal path effective during. the nonconductive. phase.

The diode rectier tube ViB is connected in series with the ground return of thesignal input circuit and is poled the sameas the diode formed by tube V1A=to conduct current on the same phase'as said diodes. Thus, during the nonconductive phase, both the tubes Vis and Vm and their wiring connections still provide capacitive coupling to the output circuits oi the dioderectifiers, namely, resistors il and 24a-and the subsequent circuits coupled thereto.

The small capacitors 2|, 22,r 23, are provided to .neutralize or balance out this `capacitive coupling to the output circuit. `During the nonconductive phase, the capacitor '2 .I and the capacitance of tube Vis are connected in series across the, input circuit, and their 'junction is connected to ground.v This forms a bridge circuit such that alternating voltages of opposite polarityappear vatpoints .I2 and I4 on opposite'sides of theinput ,circuit IIJ. By virtue of this bridge circuit, capacitor 22 neutralizesA thecathode-to-grid capacitance of tube ViA, and 23 the cathodeto-plate capacitance of tube Vis'.

Figs. 5.A-.D are simplified .diagrams of those parts of Fig. 1 that are involvedinthe.neutralization, and are shown to facilitate the explanation of this function.` Fig.y 5A- shows schematically the current..v path, and by arrows the direction-.of electron ow, during the conductive phasego'the rectifier, referringto either of the diodesin tube Figs.. 5B-D show..the, capacitive current pathsr effectiveduring. thei..non-.conductiv,e phase of the rectifier and make clear the meansfof effecting complete or. approximate balance. off the capacitive coupling as above described.

In F-ig."5B the flow of capacitive current-during the non-conductive phase is shown, the cathodegrid diodeof tube Visand the' tube Vie'facting as capacitive coupling means Cg and 1respectively The arrows in this and subseouent figures show the direction ofy capacitivecurrents -invvarious parts of the circuit at the same instant,

10 Fig. `5D shows in addition the .balancing of capacitance `Cp by capacitor .23 (Cpe) Cp denoting the cathode-plate capacitance in tubel Vis and wiring. The balancingof the capacitive coupling .paths results` in the required approximate neutralization of the tendency for radio-frequency current to be coupled to the diode. loads during the non-conductive phase.

The voltagek E4 and .,fgate voltages `referred t9,

in the specification are further. defined as a con.- ductance determining voltagecausing the rectifierflimiters` to conduct modulation for amplitude levels determined-.by the conductance voltage.

The, control ,grid-lf3 of the tube V1 is,l utilized Ain this. inventionras; an anode of one rectifier and is more specically dened as a secondary anode.

The improved system and its components comprising the preferred embodiment of the invention `may be modied'without departing from the gist andiscope of theinvention as those skilled in the` art will recognize. Therefore only such limitations as may be imposed 'by they pertinent prior art should be considered in relation to the appended claims.` `I claim: f

1. A signal coupling and amplitude limiting'system comprising rectifier means having` load impedan'ce means connected in series therewith across which alternating modulations of signal voltage appear, a second rectifierhaving anode and cathode electrodes, means coupling said vmodulations .to said second rectifier and comprising a connection from a point on said load impedance means to oneof said electrodes, the sec.- ond of said electrodes being connected t0 .an output-circuit .and second means for coupling said modulations to said second rectier and` comprising second connections from said load impedance means.. to the said. second electrode "througha phase inverter means.

2. A signal coupling and amplitudelimiting system comprising-rectifier means having -load'impedance Ameans connected in series therewith across whichA alternating vmodulation of signal voltage` appear, a second rectifier having anode and cathode electrodes, means .coupling said modulations to said second rectierand comprising aconnection .from a point o n said `load-impedance .means to one of lsaid e1ectrodes,fthe second of said electrodes :being connected'tofan output circuit, land second means forcoupling said modulations to said output circuit and-com prising --second connectionsl from .saidf loadf pedance means .to the said output circuit .through a phase inverter means. Y

3. A signal...coupling and amplitude limiting system, in accordancewithclaim;2 in which-.a conductance determining voltage means-.is provided. `and .is connected yto the saidsecondmec- .tifiereto causethelsaidC second .rectifier toconduct ,the said modulations `for amplitudes deter-mined by the.. conductance. determining voltageL of -said conductancerdetermining voltage means.

v.44A signal coupling and amplitude limiting system in accordance with c1aim2- in Whicha further rectiferhaving anode and *catho-de; electrodes in seriesy `electrical connectionk yvithlone'v `of the said means for-coupling the. said 'modulations to the 'said-output circuit provided; a conductance ldetcrmining` voltagey means. isnrcvided and -is connected to the said further rectifier causing the said further rectifier to conduct the said modulations for outward modulation amplitudes above an amplitude level determined by il the conductance determining voltage of the said 'conductance determining voltage means.

5. A signal coupling and amplitude limiting system in accordance with claim 2 in which the said phase inverter means is a reversing repeater means.

6. A signal coupling and amplitude limiting system-in accordance with claim 2 in which a portion of the said loadimpedance means is also the said phase inverter means. 7. A signal coupling and amplitude limiting system in accordance with claim 2 in which an input circuit is provided and is connected to the said rectiiier means, said rectiiier means being a variable impedance rectifier comprising a triode with cathode and secondary anode forming a rst rectifying diode and cathode and anode forming a second rectifying diode, an impedance connected in series with said rst rectifying diode across the input circuit, and an impedance connected in series with said second rectifying diode across the input circuit, whereby said :diodes with theirY series impedances operate simultaneously in parallel to rectify the voltages impressed thereon and the rectier output characteristic may be made linear by altering said impedances. 3,. A signal coupling and amplitude limiting lsystem in accordance with claim 7 in which the parallel rectifying diodes with their series impedances are connected across the said input circuit through a rectiiier and in which the undesirable capacity of the iirst diode is neutralized by a capacity connected from the secondary anode to the input. circuit and the undesirable capacity of the second diode is neutralized by a capacity connected from the plate to the input circuit.

9. A signal coupling and amplitude limiting system in accordance with claim 8 in which one element of the rectiiier coupling the two rectifying diodes to the input circuit is connected to groundand the other element thereof is connected to one end of the input circuit and in which the inherent capacity of said'rectifier is neutralized by a capacity connected from the other end of the input circuit to ground.

10. A signal coupling and amplitude limiting system, in accordance with claim 2 in which a third rectier having anode and cathode electrodes is provided and the said third rectifier electrodes are in series electrical connection with the said second means for coupling the said modulations to the said output circuit, a conductance `determining voltage means is provided and is connected to the said third rectifier causing the .system in accordance with claim 10 in which the said phase invertermeans is a reversing repeater. 12. A signal coupling and amplitude limiting system in accorda-nce with claim 10 in which a portion of the said load impedance is also the phase inverter means.

13. A signal coupling and amplitude limiting system in accordance with claim 10 in which a second conductance determining voltage means is provided and is connected to said second rectier, and the said limits oi the said modulation amplitude conductance in the said second rec- 12 tiiier and in the said third rectifier for the outward modulation amplitude cut off at amplitude levels is determined respectively` by the said conductance determining voltages of said second conductance determining voltage means and said first-named conductance determining voltage means.

14. A signal coupling and amplitude limiting system in accordance with claim 13 in which a fourth rectifier having anode and cathode electrodes in series electrical connection with one of the said means coupling the said load impedance means and the said output circuit is prof vided, a third conductance determining voltage means is provided and is connected to the said fourth rectiiier causing the said fourth rectifier to conduct the said modulations for outward modul-ation amplitudes above an amplitudelevel determined by the conductance determining 'voltage ofv said third' conductance determining 16. A signal coupling and amplitude limiting system in accordance with claim 10 in which the said third rectiiier is also in series electrical connection with the said second rectifier.

17. A signal coupling and amplitude limiting system in accordance with claim 16 in which the said second rectier and the said third rectier are in series electrical connection coupling to the said output circuit, one oi the said second and third rectiers limiting the conductance of outward modulation, and the other of said second and third rectiiiers limiting the conductance of inward modulation for the said modulations coupled in the said series electrical connection.

GILBERT J. C. ANDRESEN,

REFERENCES CITED The following references are 'of record'in the iile of this patent:

UNITED STATES PATENTS Number Name Date 1,678,653 Schroter July 31, 1928 1,908,381 Travis May 9, 1933 1,933,773 Terman Nov. 7, V1933 1,971,646 Farnham Aug. 28, 1934 2,052,613 Farnham Sept. 1, 1936 2,271,915 Belleville Fen-3, 1942 2,293,835 Y Landon Aug. 25, 1942 2,324,275 Becker July 13, 1943 2,338,418 Dallos Jan. 4, 1944 2,418,389 Andresen Apr. l, 1947 2,422,976 Nicholson June 24, 1947 2,423,263 Sprague July v1, 1947 2,423,671 Wolff July `8, 1947 `2,453,953 Andresen Nov. 16, 

